1. Field of the Invention
The present invention relates to a direct fuel injection-type spark ignition internal combustion engine.
2. Description of the Related Art
A direct fuel injection-type spark ignition internal combustion engine with a fuel injector for injecting fuel directly into cylinder forms a combustible mixture only in the vicinity of a spark plug at the ignition timing by injecting fuel in the latter half of the compression stroke to realize stratified charge combustion by which a lean mixture in the cylinder as a whole can be burned.
Thus, the stratified charge combustion is effective to reduce the fuel consumption. However, fuel injected in the compression stroke must be vaporized for a relatively short period until the ignition timing, and thus in high engine load operating conditions in which a large amount of fuel is required, a general direct fuel injection-type spark ignition internal combustion engine abandons stratified charge combustion and carries out uniform charge combustion in which a uniform charge mixture is formed in the cylinder at the ignition timing by injecting fuel in the intake stroke.
In a general spark ignition internal combustion engine including such a direct fuel injection-type spark ignition internal combustion engine, an intake port and an exhaust port are connected to the top portion of the cylinder. Therefore, when the intake valve is opened in the intake stroke, intake air is introduced from the whole circumference portion of opening of the intake port into the cylinder and thus a tumbling stream of intake air which generally turns in the cylinder is formed, which stream moves down along the exhaust port side of the cylinder bore and moves up along the intake port side thereof.
Such a vertical tumbling stream can be made strong or weak by changing a connecting direction of the intake port to the top portion of the cylinder or a configuration of the intake port. If the tumbling stream is made strong, in uniform charge combustion, fuel injected in the intake stroke is satisfactorily mixed with intake air by the tumbling stream and thus a good uniform charge mixture can be formed in the cylinder at the ignition timing. However, the strongly tumbling stream still turns when the piston moves up in the first half of the compression stroke, and does not disappear in the latter half of the compression stroke so that turbulence is produced in the cylinder. Therefore, in stratified charge combustion, a combustible mixture in the vicinity of the spark plug is broken up before the ignition timing and thus it becomes difficult to realize good stratified charge combustion. On the other hand, if the tumbling stream is made weak, the problem in which a combustible mixture is broken up in stratified charge combustion can be solved, but in uniform charge combustion, the injected fuel is not satisfactorily mixed with intake air by the tumbling stream and thus good uniform charge combustion cannot be realized.
Japanese Unexamined Patent Publication (Kokai) No. 10-252477 discloses a direct fuel injection-type spark ignition internal combustion engine in which, in stratified charge combustion, the fuel injector arranged on the intake valve side in the upper portion of the cylinder injects fuel into a cavity formed on the upper surface of the piston in the latter half of the compression stroke. In the internal combustion engine, a mask wall is formed on the opening of the intake port only at the side adjacent to the exhaust port and, in stratified charge combustion, a lifting amount of the intake valve is reduced by use of a variable lifting mechanism.
Therefore, in stratified charge combustion, intake air is introduced from the opening of the intake port only at the opposite side of the mask wall into the cylinder and thus another tumbling stream of intake air which generally turns in the cylinder is formed, which stream moves down along the intake port side of the cylinder bore and moves up along the exhaust port side thereof. This tumbling stream turns in reverse in comparison with the above-mentioned tumbling stream. Accordingly, in hereafter, this tumbling stream is defined as the reverse tumbling stream, and the above-mentioned tumbling stream is defined as the original tumbling stream.
Thus, the reverse tumbling stream formed in the cylinder in stratified charge combustion is relatively strong to be produced during the whole intake stroke. Therefore, the reverse tumbling stream still turns vertically in the cylinder in the compression stroke and enters into the cavity involving the moving up of the piston, and thereafter turns vertically in the cavity in the latter half of the compression stroke. The internal combustion engine of the above-mentioned prior art intends to lead fuel vaporized in the cavity to the vicinity of the spark plug by the reverse tumbling stream and to form a combustible mixture therein.
However, even if the relatively strong reverse tumbling stream leads fuel vaporized in the cavity to the vicinity of the spark plug, it also functions to break up the combustible mixture so that good stratified charge combustion cannot be realized. Thus, in stratified charge combustion, if a turbulence due to the original tumbling stream or the reverse tumbling stream is in the cylinder at least in the latter half of the compression stroke, a combustible mixture in the vicinity of the spark plug may be broken up and thus this is unfavorable in stratified charge combustion.
Therefore, an object of the present invention is to provide a direct fuel injection-type spark ignition internal combustion engine which carries out changes to stratified charge combustion and uniform charge combustion, and which can prevent a turbulence in the cylinder in the latter half of the compression stroke when stratified charge combustion is carried out and can form a good uniform charge mixture in the cylinder by satisfactory mixing in the intake stroke when uniform charge combustion is carried out.
According to the present invention, there is provided a first direct fuel injection-type spark ignition internal combustion engine comprising a spark plug and a fuel injector for injecting fuel directly into the cylinder, wherein the engine can carry out stratified charge combustion by the fuel injection in the compression stroke and uniform charge combustion by the fuel injection in the intake stroke, the engine comprising variable tumbling stream strength means which can make a tumbling stream formed in the cylinder in the intake stroke in said stratified charge combustion weaker than that in said uniform charge combustion.
According to the present invention, there is provided a second direct fuel injection-type spark ignition internal combustion engine comprising a spark plug and a fuel injector for injecting fuel directly into the cylinder, wherein the engine can carry out stratified charge combustion by the fuel injection in the compression stroke and uniform charge combustion by the fuel injection in the intake stroke, fuel is injected in the first stage of the intake stroke in the uniform charge combustion, the engine comprising flow producing means which can produce a strong flow in the cylinder only in the first stage of the intake stroke.
The present invention will be more fully understood from the description of preferred embodiments of the invention set forth below, together with the accompanying drawings.